These researches are directed at finding a practical method for identifying infants and young children who are at risk of developing amblyopia due either to uncorrected refractive errors or subtle motor problems. They are also aimed at finding the physiological basis of an effective preventative therapy for refractive amblyopia and severe ametropia by investigating emmetropizing mechanisms in humans and animals. To accomplish these goals it is proposed to conduct both human and animal studies on refractive development. In the human work, our 15 year longitudinal study of refractive development will be extended by refracting infants and children of our volunteer population with visible light photorefractive and infrared autorefractive methods. In particular a new binocular infrared autorefractive method, developed partially in our laboratory, will be employed. Data on parental and familial refractive status will also be gathered. This refractive data will be used to construct a practical method for the prediction and, hopefully, the prevention of amblyopia on the basis of refractive and motor behavior measured in infancy. The laboratory's animal work will continue to concentrate on the study of the growth of eyes of chicks, focusing now on the image-directed regulation of growth of the anterior chamber. We will investigate the nature of the compensation for astigmatic defocus, and we will employ conditions of constant light to isolate one of the two important feedback mechanisms of image controlled growth. We will also examine the optical methods by which the chick eye maintains optical quality during accommodation in the face of a large change of aberration structure of the cornea. From a knowledge of the emmetropization mechanisms of chicks, we hope to gain insights into both the normal and the pathological development of human refractive states.